The WHO has targeted malaria amongst the five most devastating diseases worldwide. Malaria accounts for over 600 million new cases and more than 2 million deaths annually. The most dangerous species of parasite causing malaria is Plasmodium falciparum. This species may cause neurovascular involvement leading to coma and death. The life cycle of this parasite is complex. It includes various parasite forms which under go transitional changes for infective and replicative purposes both in the arthropod vector, the mosquito, and in the human host, as liver (exoerythrocytic) and blood (erythrocytic) stage forms of the parasite. Little is known about the initiation of gametocytogenesis (switch from asexual to sexual blood stage) or gametogenesis (switch from sexual blood stage to sexual mosquito stage). It is thought that these transitional charges are mediated by second messenger enzymes and signaling proteins. To determine the mechanism of transcriptional control of these differentiation events we have been isolating cDNA and genomic clones in attempts to identify the players responsible in P falciparum. Currently, we have isolated and are characterizing a gene encoding a signal transduction controlling protein under calcium regulation and tyrosine kinase control, homologous to sarcalumenin and eps-15 in other organisms. In Northern blot analysis transcript was detected in gamete and early ring stage parasites with little or no transcript detected in the other erythrocytic stages. To clarify these findings, immunofluorescence imcroscopy and Western blotting analysis using polyclonal rabbit antibody directed against synthetic peptides are being performed. Inhibitor/enhancer studies are planned in attempts to alter in vitro development. The regulation of this protein may directly effect the signal transduction pathways involved in sexual differentiation of this medically important parasite. With the current ability to transfect Plasmodium falciparum parasites in vitro, we hope to produce Gain-of-Function a well as Loss-of-Function mutants. Ultimately, understanding the regulatory events responsible for stage differentiation may provide further insight into disrupting the normal life cycle of this deadly parasite.